linux-kernel - Re: [PATCH -tip 2/2] x86/hweight: Use POPCNT when available with X86_NATIVE

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Message-ID: <20250325171141.GDZ-LjzaPbAG1MwjZi@fat_crate.local>
Date: Tue, 25 Mar 2025 18:11:41 +0100
From: Borislav Petkov <bp@...en8.de>
To: Uros Bizjak <ubizjak@...il.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH -tip 2/2] x86/hweight: Use POPCNT when available with
 X86_NATIVE_CPU option

On Tue, Mar 25, 2025 at 05:48:38PM +0100, Uros Bizjak wrote:
> +#ifdef __POPCNT__
> +	asm_inline (ASM_FORCE_CLR "popcntl %[val], %[cnt]"
> +		    : [cnt] "=&r" (res)
> +		    : [val] ASM_INPUT_RM (w));
> +#else
>  	asm_inline (ALTERNATIVE(ANNOTATE_IGNORE_ALTERNATIVE
>  				"call __sw_hweight32",
>  				ASM_CLR "popcntl %[val], %[cnt]",
>  				X86_FEATURE_POPCNT)
>  			 : [cnt] "=a" (res), ASM_CALL_CONSTRAINT
>  			 : [val] REG_IN (w));
> -
> +#endif

A whopping 599 bytes which makes the asm more ugly.

Not worth the effort IMO.

-- 
Regards/Gruss,
    Boris.

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